The invention discloses a double-thread rotary electric arc sensor applied to the field of welding automation, robot welding and automatic tracking of welding lines. The double-thread rotary electric arc sensor mainly comprises a small-size wire feeding machine, a fork-shaped main conductive rod, a secondary conductive rod, a driving mechanism, a conductive rod swinging fixing mechanism, an eccentric adjusting mechanism and a shell body. When the driving mechanism moves, the fork-shaped main conductive rod and the wire feeding machine are driven to rotate synchronously, and the secondary conductive rod does tapered rotation along the main conductive rod, so that a double-thread rotary electric arc is formed. Compared with the prior art, the double-thread rotary electric arc sensor has the following advantages and prominent effects that the problem of winding a double-thread rotary electric arc welding wire is solved, and the welding speed and the welding efficiency are improved; and in application of vertical position welding and over-head position welding, the flowing and dropping of a molten pool can be reduced under the condition of ensuring a certain welding speed and the quality of welding lines is improved.